This invention relates to stabilization of compositions containing cooked meat, especially turkey-gravy compositions and vegetables-meat-sauce compositions, against the development of toxins from pathogenic bacterial contaminants. The stabilized compositions are attained by the incorporation of nisin-containing whey derived from a nisin-producing culture. The invention also relates to methods of stabilizing food compositions containing cooked meat and/or cooked meat and vegetables in a sauce against the development of toxins, wherein the method comprises adding nisin-containing whey derived from a nisin-producing culture to the cooked meat or cooked meat, vegetables, and sauce combination.
Packaged precooked meat and gravy combinations are commonly available to the public in vacuum sealed airtight packets, such as those made of pliable plastic films. The packets are termed airtight to the extent that the films are relatively impermeable to air, so that the components sealed within them at the time of preparation remain largely anaerobic. Such products must be prepared free of pathogenic organisms, especially toxin-producing anaerobes. Pathogenic organisms that may contaminate packaged meats include, by way of nonlimiting example, Clostridium botulinum, C. perfringens, (Lucke et al., in xe2x80x9cEcology and Control Foodsxe2x80x9d (A. H. W. Hauschild and K. L. Dodds, eds.) Marcel Dekker, New York, 1993, pp. 177-207; Smart et al., J. AppI. Bacteriol. 46, 377-383 (1979); Roberts et al., J. Fd. Technol., 14, 211-226 (1979); Tompkin, Food Technology, 34, 229-236, and 257 (1980); Bryan et al., Amer. Public Health, 61, 1869-1885 (1971); Microbial Ecology of Food Commoditiesxe2x80x94Microorganisms in Foods 6: Blackie Academic and Professional, 1998, p. 115), Listeria monocytogenes, Escherichia coli, Bacillus cereus, Enterococcus faecalis, and similar microorganisms. Among these, spore-forming, toxin-producing microorganisms are of particular concern, because any spores produced by viable cells may survive and grow to produce toxins subsequent to manufacturing or domestic heating steps. Such microorganisms include species of the genus Clostridium.
In U.S. Pat. Nos. 4,888,191 and 5,017,391, Anders et al. disclose compositions and methods related to the use of lactate salts to delay C. botulinum growth in a foodstuff such as fish or poultry. The foods are heated to a temperature sufficient to cook the meat but not to sterilize the product. Anders et al. suggest that lactate may be used alone, or in combination with other agents such as sodium nitrite. These patents fail to discuss nisin or its properties.
Maas et al. (AppI. Envir. Microbiol., 55, 2226-2229 (1989)) report that lactate, when incorporated into a turkey meat vacuum-packed composition, delays the generation of botulinum toxin in a manner directly dependent on the concentration of lactate introduced into the composition. Maas et al. do not mention nisin.
Nisin is a peptide-like antibacterial substance produced by microorganisms such as Lactococcus lactis subsp. lactis (formerly known as Streptococcus lactis). Its structure is illustrated in U.S. Pat. No. 5,527,505 to Yamauchi et al. The highest activity preparations of nisin contain about 40 million IU per gram. Commercial preparations of nisin are available. For example, one commercial preparation, NISAPLIN(trademark), containing about 1 million IU per gram is available from Aplin and Barrett Ltd., Trowbridge, England; another commercial preparation, CHRISIN(trademark), containing about 1 million IU per gram is available from Chr. Hansen A/S (Denmark). Nisin has no known toxic effects in humans. It is widely used in a variety of prepared dairy foods. Experimental use in preserving other foods has also been reported. Details on these applications are provided below.
A number of efforts have been reported since 1975 directed to reducing uncoupled acid production in dairy fermentations by controlling the post-fermentation acidification of yogurt. In some of these studies, a nisin producing culture was introduced in an attempt to inhibit these effects. Kalra et al. (Indian Journal of Dairy Science, 28: 71-72 (1975)) incorporated the nisin producing culture Streptococcus lactis (now known as L. lactis subsp. lactis) along with the yogurt culture before fermentation. Others introduced nisin in milk prior to fermentation (Bayoumi, Chem. Mikrobiol. Technol. Lebensm., 13:65-69 (1991)) or following fermentation (Gupta et al., Cultured Dairy Products Journal, 23: 17-18 (1988); Gupta et al., Cultured Dairy Products Journal, 23: 9-10 (1989)). In all cases, the rate of post-fermentation acidification was only partially inhibited by these treatments and the yogurt continued to become more acidic throughout its shelf life.
In U.S. Pat. No. 5,527,505, by Yamauchi et al., yogurt was produced from raw milk by incorporating a nisin-producing strain, Lactococcus lactis subsp. lactis, along with the traditional yogurt culture consisting of Streptococcus salivarius subsp. thermophilus (ST) and Lactobacillus delbrueckii subsp. bulgaricus (LB). Yamauchi et al. teach that the lactococci are needed to secrete the nisin, whose effect is to retard the activity of ST and LB. The resulting yogurt therefore contains the lactococci used to produce the nisin. Nonetheless, the acidity of yogurt containing the nisin-producing bacteria increased by 64 to 96 percent in 14 days, in various experiments inoculated with differing amounts of L. lactis subsp. lactis, compared to the initial acidity at the completion of fermentation. Other studies (Hogarty et al., J. Fd. Prot., 45:1208-1211 (1982); Sadovski et al., XX International Dairy Congress, Vol. E: 542-5-44 (1978)) also noted acid production and development of bitterness at low temperature by some mesophilic starter lactococci in dairy products.
In U.S. Pat. No. 5,015,487 to Collison et al., the use of nisin, as a representative of the class of lanthionine bacteriocins, to control undesirable microorganisms in heat processed meats is disclosed. In tests involving dipping frankfurters in nisin solutions, the growth of L. monocytogenes was effectively inhibited upon storage at 4xc2x0 C.
Chung et al. (Appl. Envir. Microbiol., 55,1329-1333 (1989)) report that nisin has an inhibitory effect on gram-positive bacteria, such as L. monocytogenes, Staphylococcus aureus and Streptococcus lactis, but has no such effect on gram-negative bacteria such as Serratia marcescens, Salmonella typhimurium and Pseudomonas aeruginosa when these microorganisms are attached to meat.
Nisin has been added to cheeses to inhibit toxin production by Clostridium botulinum (U.S. Pat. No. 4,584,199 to Taylor). U.S. Pat. No. 4,597,972 to Taylor discloses a detailed example in which chicken frankfurter components are shown to require the presence of both added nitrite and added nisin in order to prevent or delay botulinum toxin production when challenged with C. botulinum. 
Nisaplin(trademark) has been found to preserve salad dressings from microbiological contamination, such as challenge by Lactobacillus brevis subsp. lindneri, for an extended shelf life period (Muriana et al., J. Food Protection, 58:1109-1113 (1995)).
There remains a need for compositions and procedures related to prepared meat products that inhibit the growth of pathogenic microorganisms, and the production of toxins by them, using natural or innocuous ingredients. In particular, there is a need for such compositions and methods that avoid the introduction of nitrite, the use of which has been the subject of extended controversy. There also remains a need for high moisture compositions and procedures related to food products containing meat and vegetables in a sauce that inhibit the growth of pathogenic microorganisms, and the production of toxins by them, using natural or innocuous ingredients. The present invention addresses these needs.
The present invention provides a stabilized preparation of cooked meat comprising cooked meat and nisin-containing whey. The present invention also provides a stabilized preparation of cooked meat and vegetables comprising cooked meat, vegetables, sauce, and nisin-containing whey. In an important embodiment, the nisin-containing whey is prepared by inoculating a pasteurized dairy composition with a culture of a nisin-producing microorganism, incubating the composition until the pH attains a value between about 6.2 and about 4.0 and a whey and curd mixture is formed, and separating the whey from the whey and curd mixture to give the separated whey which is the nisin-containing whey. In an alternative embodiment, the nisin-containing whey is obtained from the fermentation of a fortified cheese whey composition using a nisin-producing microorganism. The invention also provides a method of making a stabilized preparation of cooked meat, that includes preparing a composition including meat and nisin-containing whey, and cooking the composition. The invention also provides a method of making a stabilized preparation of cooked meat and vegetables in a sauce, that includes preparing a composition including meat, vegetables, sauce, and nisin-containing whey, and cooking the composition. The invention additionally provides a method of inhibiting the growth of a pathogenic microorganism in cooked meat that includes preparing a composition comprising meat and nisin-containing whey, sealing the cooked composition into packaging, and cooking the composition, whereby the growth of a pathogenic microorganism is inhibited. The invention additionally provides a method of inhibiting the growth of a pathogenic microorganism in food compositions comprising cooked meat and vegetables in a sauce that includes preparing a composition comprising meat, vegetables, sauce, and nisin-containing whey, cooking the composition, and sealing the cooked composition into packaging, whereby the growth of a pathogenic microorganism is inhibited. The stabilized food products of this invention do not require, and preferably do not contain, preservatives or stabilizers such as added nitrite salts.
In important embodiments of the preparation and methods of the invention, the growth of microorganisms chosen from the group consisting of Clostridium botulinum, C. perfringens, Listeria monocytogenes, Bacillus cereus, Staphylococcus aureus, and Enterococcus faecalis is inhibited, and in a more preferred embodiment, the inhibited microorganism is C. botulinum. In yet additional preferred embodiments, the cooked meat is beef, pork, lamb, poultry, fish, seafood, or a mixture thereof, more preferably, the cooked meat is poultry such as turkey, chicken, duck, or a mixture thereof; yet more preferably, the poultry is turkey or chicken. In further preferred embodiments, the stabilized preparation additionally includes a gravy, and furthermore contains no nitrite salts. In additional preferred embodiments of the preparation and methods, the nisin-containing whey is added to the cooked meat or cooked meat-gravy combination in a proportion from about 10 to about 50 percent by weight, and more preferably this proportion is about 25 to about 35 percent by weight. In further preferred embodiments, the stabilized preparation includes cooked meat and vegetables in a high moisture sauce. In additional preferred embodiments of the preparation and methods, the nisin-containing whey is added to the cooked meat-vegetable combination in a proportion from about 2 to about 50 percent by weight, and more preferably this proportion is about 5 to about 15 percent by weight. Preferably, the amount of nisin-containing cultured whey added to cooked meat, cooked meat/gravy combination, or cooked meat/vegetable combination is sufficient to provide at least about 150 IU nisin/g, more preferably about 200 to about 1200 IU nisin/g, and most preferably about 300 to about 700 IU nisin/g. The vegetables include yellow, orange, and red vegetables, such as carrots, various type of peppers, broccoli, various types of peas and pea pods, cauliflower, onions, tomatoes, mushrooms, zucchini, corn, celery, asparagus, green beans, water chestnuts, bamboo shoots, various types of oriental vegetables, and the like.